Behavioral Adaptations to Parasites: Are Wood Rats Using Plant Essential Oils to Control Nest Ectoparasites?

Several species of birds use fresh aromatic foliage in their nests to reduce the abundance of ectoparasites. Some dusky-footed wood rats bring bay leaves into their stick houses and selectively place them around the edge of their sleeping nests. Bay leaves contain monoterpenes, which are effective in killing fleas. In this study we asked whether wood rats use other plant materials with flea-killing potential to build the sleeping nest itself.

&emsp;We studied wood rat nests from several distinct habitats at two locales in California. We used iButton data-loggers to monitor temperature and humidity in the immediate vicinity of sleeping nests, used activated charcoal strips to capture and identify volatiles in the nest chamber, and collected nest material for study. We sealed nest material in airtight cans with a charcoal strip to identify volatiles within the nest material itself. We extracted ectoparasites from nest material samples to estimate their abundance.

&emsp;Through gas chromatography mass-spectrometry (GCMS) analysis, we found that nest material exuded a number of monoterpenes and sesquiterpenes not previously detected. We evaluated some of these terpenes for their flea-killing potency under standard bioassay conditions and under temperature and humidity regimes that more closely resemble those in the sleeping nest environment. Cineole, a monoterpene abundant in bay with strong flea-killing capacity, was used as a reference with which to compare the new volatiles. Of the new substances we have tested, cymene, isolongifolene, camphene, nonanal, sabinene, and limonene, only three caused significant flea mortality, e.g. cymene (p&lt;0.01), sabinene (p&lt;0.01), and limonene (p&lt;0.05). All three are significantly less potent than cineole but strong enough to be of interest. We are continuing to evaluate the potency of the sesquiterpenes and whether there is a relationship between the number of ectoparasites and volatiles found in the nest.

**This work was supported in part by the Merck/AAAS Undergraduate Science Research Program.